HelpPC 2.10	Quick Reference Utility	Copyright 1991 David Jurgens
double tan( double y, double x )        - prototype in math.h        - returns arc tangent of x*2        - used instead of atan when the resulting angle is near          pi/2 or -pi/2
Esc or Alt-X to exit	atan2	Home/PgUp/PgDn/End ←↑↓→